1. Field of the Invention
The present invention generally relates to a scale device such as a position detector, digital scale device, encoder or the like annexed to a machine tool; industrial machine, precision machine or the like to detect positional information such as a relative travel, position and the like of a moving part of such machines. More particularly, the present invention is directed to a dustproof structure of the scale device including a case member having a scale member housed therein and a carrier unit which slides relative to the case member.
This application claims the priority of the Japanese Patent Application No. 2002-295081 filed on Oct. 8, 2002, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
Generally, on machine tools, industrial machines, precision machines, etc., there is installed a scale device which detects positional information such as a travel, position, etc. of a moving part such as a table or the like. The position of the moving part is controlled based on a detection output from the scale device. The scale device includes a long scale member having an optical, magnetic or mechanical position signal provided thereon and fixed to a stationary part of a machine on which the scale device is to be used, a detector unit sliding relative to the scale member and in conjunction with a movement of the moving part of the machine, and a sensor provided in the detector unit to detect the position signal.
In the scale device, the scale member is housed in a case member fixed to the stationary part of the machine, and a carrier unit is installed to the moving part of the machine. Inside the case member, the detector unit is slidably disposed with the sensor directed opposite to a signal recording surface of the scale member, and the detector unit is coupled by a coupling member to the carrier unit. A guide opening is formed in the lateral side of the case member correspondingly to an area on the scale member where the position signal is formed, and the coupling member is slidably penetrated through the guide opening.
Since the scale member and detector unit are thus housed in the case member, the scale device is capable of high-accuracy measurement and detection with the position signal being protected against dust. The scale device has additionally provided thereon a sealing mechanism which seals the guide opening along its full length while allowing the coupling member to move slidably through the guide opening formed in the case member. There has been proposed a sealing mechanism including a pair of seal lip members which close the guide opening along its full length (see the Japanese Patent Publication No. 2911746 cited as reference herein, for example).
Referring now to FIG. 1, there is illustrated in the form of a top axial-sectional view the substantial part of the sealing structure of a conventional scale device. The scale device is generally indicated with a reference number 100. As shown in FIG. 1, the scale device 100 includes a case member 101 having a guide opening 102 formed therein, and a pair of seal lip members 103 and 104 formed from a synthetic resin or rubber and installed to inner surfaces, respectively, of the case member 101 (namely, across the guide opening 102). The slip lip members 103 and 104 are installed inside the case member 101 (namely, across the guide opening 102) for end portions 103a and 104a thereof to be in elastic contact with each other. The seal lip members 103 and 104 are in elastic contact with opposite sides of a coupling member 106 which provides a coupling between a carrier unit 105 and a detector unit (not shown). Even when the coupling member 106 slides in the guide opening 102, the seal lip members 103 and 104 are put into elastic contact, at end portions 103a and 104a thereof corresponding to the sliding distance of the coupling member 106, with the respective opposite sides of the coupling member 106 and thus keep the guide opening 102 closed.
References Cited Herein:
1. Japanese Patent Publication No. 2911746
In the scale device 100, the coupling member 106 is to move sliding in the guide opening 102 while spreading out the end portions 103a and 104a of the seal lip members 103 and 104. To this end, the coupling member 106 is shaped to have a thickness gradually reduced from the center toward opposite longitudinal ends 106a and 106b thereof in the sliding direction. Namely, it has a generally boat-shaped section.
As above, the scale device 100 is constructed such that the seal lip members 103 and 104 are in elastic contact, at the end portions 103a and 104a thereof, with the respective opposite sides of the coupling member 106 to close the guide opening 102. However, because the coupling member 106 is still thick at opposite end portions 106a and 106b thereof as shown in FIG. 2, the end portions 103a and 104a of the seal lip members 103 and 104 will not be in full elastic contact, at the end portions 106a and 106b, with the coupling member 106, which results in gaps 107a and 107b at such portions. The function of the sealing mechanism of the scale device 100 is thus impaired and dust or the like will come into the gaps 107a and 107b. The dust will possibly lower the accuracy of measurement and detection, and damage the position signal recorded on the scale member.